Causality
by tfm
Summary: David Rossi had never really believed in fate, but then time travel had gone and made him change his mind. AU. Pre-Rossi/Prentiss.


**Title: **Causality  
**Rating: **PG**  
Fandom: **Criminal Minds**  
Characters/Pairing: **pre-Rossi/Prentiss**  
Genre: **Science Fiction/Drama/Humor**  
Summary: **David Rossi had never really believed in fate, but then time travel had gone and made him change his mind. AU.  
**Prompt: **From mingsmommy: time traveling BAU to solve crimes throughout time  
**Author's Note: **I've started a prompt list, because I've got summer holidays coming up (in like, a month) and I'd like some one-shots to work on. If you're interested in providing a prompt, go right ahead; no pairing restrictions, but obviously, if it's too insanely creepy, chances are I won't write anything for it.

*****

_You mustn't interfere with the past! Don't do anything that affects anything. Unless it turns out you were supposed to do it. In which case, for the love of God don't not do it! _

_**Professor Hubert J. Farnsworth**_

*****

David Rossi woke up to a headache.

Of course, it was his own stupid fault. The previous night, he and Derek had "borrowed" a pair of Time Units in order to partake in the festivities of the last turn of the millennium. Fate had conspired against him, though. They'd almost lost the Time Units to a couple of drunken young co-eds with whom Derek had been flirting, and were forced to go on an alcohol-fuelled quest with the local Gatekeepers to get the devices back. The ordeal had earned him both the mother of all hangovers, and a reprimand from Section Chief Strauss upon their return.

'In my defence, Erin,' he'd argued (still slightly drunk), 'History was already written. By _not_ going back, I stood the chance of being responsible for the implosion of the universe.'

Apparently, though, it wasn't a good enough excuse, and they were both on Probation for the next two months.

Probation wasn't really as bad as they made it out to be, or at least, that was what Dave thought. Instead of solving cold cases, they were reduced to observing the behavior of convicted killers in order to further increase their repertoire of knowledge. It meant sitting around with a clipboard, and taking notes.

Derek, naturally, was a little more upset by this news. Kicking ass and taking names was a little more the younger agent's style. David Rossi remembered _those_ days.

He slid out of bed, pausing only at the espresso machine on his way to the shower. The coffee would be made by the time he'd finished showering, and he could let some much-needed caffeine burn through his system. Spencer probably would have argued that with a hangover, coffee was the last thing he should have been drinking, but quite frankly, Dave didn't care.

Before dressing, he checked the assignment listings on his laptop; he was going to 2048 today, to take notes on a minor biological attack. The listing also provided helpful hints on the dress code of the time, which he dutifully ignored. It wasn't as though he was going to don a Zoot suit for the occasion.

He ran into Derek in the hallway on his way to the briefing room. The younger Agent was dressed in a neon kilt, and had a less than amused look on his face.

'Cyberpunk wars of 2350?' Dave guessed, to which Derek nodded glumly.

'This is what I get for trying to have a good time.'

'Well, you did almost compromise the operation for the sake of a little T&A.'

'Come on, man,' said Derek, exasperated, 'They offered me a threesome. Who am I to say no to that?'

Dave shook his head. 'A woman responds better if you treat her with respect.'

Derek didn't have time to respond, as it was at that point that they reached the briefing room. Spencer and Penelope were waiting for them there, the two techies engaged in what seemed to be an in-depth discussion of the Mesoproterozoic Era.

'My hunk 'o spunk,' Penelope squealed the moment she saw Derek. 'Oh, you look adorable. Promise to take lots of pictures for me?' she pouted, adding, after a moment's consideration, 'For research purposes, of course?'

'You know it, baby girl,' he grinned, any despair having immediately evaporated at the sight of Penelope.

Spencer gave Dave an awkward shrug. 'I guess you're stuck with me as your tech again,' he said, somewhat apologetically.

'Spence, I trust a man that can recite the theories of self-consistent time travel much more than I trust some kid that got a job because he almost accidentally blew a hole in the space-time continuum while trying to convince himself not to marry his first wife.' The comment got the desired laugh – the "kid" of course, had been Rossi, some thirty years ago (on a linear timeline. To judge his age based on how often he had gone back and forth in time would require a physicist, a mathematician, and a twelve year supply of various psychostimulants).

Spencer led him to one of the small rooms that jutted off the briefing area. Because he was only going to observe, he didn't need a full briefing – just a rundown of the time and location he was signed off to observe.

'Once you arrive in your designated time period, the Gatekeepers of that era will accompany you on your mission, but will not intervene unless the situation becomes critical. Any attempts at disclosing your status as a member of the Federal Bureau of Investigation's Time-Traveling Division will result in disciplinary measures outlined in Section 232B of the Handbook...'

Dave zoned out as Spencer recited the mandatory pre-travel doctrine.

'As this is an observation only mission, your time limit will be four hours. If you require more time to complete the mission objectives, the Gatekeeper in charge will examine your case before assigning extra time, if it's deemed necessary.'

Dave suppressed a smirk. It was the Gatekeepers that had extended their stay indefinitely the previous night, the Agents having joined them in their drunken festivities.

Spencer handed him the Time Unit, and he strapped it around his wrist. The room was something of a Faraday Cage; no signal could get in, no signal could get out. There would be no interferences as the machine sent him to 2048. Spencer gave him a brief wave. 'I'll see you when you get back,' he said. 'No losing the Time Unit, this time,' he added, with the briefest of smirks. 'Strauss'll ban you indefinitely.'

'I'll keep that in mind,' Dave called out, as the door clicked shut. He briefly checked the settings on the Time Unit (a newbie had once accidentally sent him back to the Middle Ages by mistake) before pressing the green button on the side of the device.

The world dropped away around him.

*

Even though he'd been doing it for some (the exact amount, as aforementioned, was indeterminable), jumping through time was something that David Rossi had never quite gotten used to. Technically speaking, he wasn't traveling into the past, _or_ into the future; the starting point had been somewhere outside of both time and space, and it was just a matter of pinpointing the right place to jump into the pool that was the universe.

When the world stopped spinning, he fell backwards against the wall of the small room. Technically speaking, he hadn't actually done anything, but the process of time travel took a lot out of every Agent.

He pressed the button by the steel door, and waited for retrieval. He was vaguely aware of the door opening, and a bottle of some liquid being thrust into his hand. He took the proffered bottle, and drunk like a fish. The liquid was supposed rehydrate and replenish, and he slowly felt the strength trickling back into him.

'July 21st, 2048? New Haven City?' he asked the figure whose face he couldn't quite make out yet. '12.27pm?'

'12.28, now,' the figure said, taking Dave's arm and leading him out of the small room. He blinked against the sudden brightness, and it was several seconds before he could focus his attention on the two other people in the room. The one holding an empty bottle in her hand was blond, straight hair just brushing her shoulders. Her partner was tall, with short, dark hair. They introduced themselves as Jennifer and Aaron.

'They sent you back to observe?' asked Jennifer, once he'd regained his composure. 'There must be a budget surplus.' There was something of a devious look on the Gatekeeper's face, to which her partner said:

'The moment you go back, she's going to send a requisition form for seven thousand gas masks.'

Dave raised an eyebrow. Jennifer shrugged.

'It gets a little boring. The moment this decade's up, though, I'll find out whether my full Probation has been revoked yet.'

'Yeah? What'd you do to get that?' Dave asked, wondering how much worse it was than his jaunt back to 1999 for the Y2K celebrations.

'I uh...started a war.'

In the background, Aaron shook his head silently, the beginnings of a smirk on his face. 'Jen, prep the squad car. I'll brief Agent Rossi.'

Jennifer gave a shrug, and waved goodbye.

'I have something for you,' Aaron said, as soon as his partner had left the room.

Dave raised an eyebrow. 'I beg your pardon?'

'Don't ask me any questions. Just take it. That's all I can tell you.' He handed over the small piece of paper. It looked a little worn around the edges – looked at least a couple of years old. He careful unfolded it, and stared at the short message, written in neat capitals.

"Save her."

*

The problem with time travel was that he had absolutely no way of knowing who had left the note. It could have been an ally, it could have been a rogue agent, it could have been any number of antagonistic forces that wanted him to do something that he might not otherwise have done.

Still, he took some solace in knowing that whatever path he chose, there was no other path he could have chosen. Time was a fixed variable. It was logical. Each event in the past foretold the future. In a way, it was far less complicated than the alternate universes theory of time travel, but the downside (which often became an upside) was that there was no way of changing the past.

_Anything that happens, happens. Anything that, in happening, causes something else to happen, causes something else to happen. Anything that, in happening, causes itself to happen, happens again. It doesn't necessarily do it in chronological order though._ They were words that Spencer took great care in reciting over and over again, along with a plethora of other witty quotes from sources of a science-fiction origin.

Instead of worrying over it, Dave simply slipped the note into his pocket, and reminded himself to worry about it later. First, he had a job to do.

'No interference,' Aaron reminded him, as they came upon the scene of the future biological attack. This event has always happened, and it always will happen. Anything we do only serves to facilitate its occurrence.'

'This isn't my first rodeo,' was all Dave said.

'I understand that,' Aaron told him. 'But I have to say it anyway. It's a lot of paperwork if you decide to try and change history.'

'I _can't_ change history,' he pointed out.

'I know. That doesn't stop some people from trying,' Aaron gave a small shrug.

Jennifer handed him a pill, adding, 'This will protect you from the biological agent. You can't report back on terrorist techniques if you're dead, right?'

Dave shrugged, but dry-swallowed the pill anyway. Once upon a time, he might have questioned the ethics of possessing a preventative measure for a biological agent and yet doing nothing to stop the dozens of deaths that could potentially follow. He hadn't actually looked at the history regarding the event; knowing what was supposed to happen made him feel a little less in control of his own actions.

'FBI! Freeze!'

'Here we go,' muttered Jennifer, as Dave diligently watched the scene in front of him, notebook in hand. He'd passed the camera from his kit bag across to Aaron, who had agreed to take care of the photographic documentation end of things.

The events played out like a movie; things were happening, and there was no way he could change the outcome. He watched as the FBI agents surrounded their suspect, a man with a heavy backpack slung over his shoulders. One of the agents caught his eye; she was dark-haired, pale-skinned – in an attractive way – and he was fairly sure that she was about to die.

Save her.

The moment the shit hit the fan, he found himself moving forward. He heart both Aaron and Jennifer calling out to him – telling him to stop – but the words fell on deaf ears. He didn't know what he was doing. He didn't even know why he was doing it. He just knew that he had to do it.

The biological agent had dispersed quickly, the FBI personnel succumbing to it first. The man who had set off the device was lying dead, a bullet-hole in his chest. Too little, too late.

He put his fingers to her neck, feeling the tiniest flutter of heartbeats. A heavy hand landed on his shoulder.

'David.' Aaron's brow was furrowed in frustration. 'What the hell are you doing?'

'You read the note, didn't you? You know what I have to do.'

'You don't know that.'

'Well I'm doing it, aren't I?' he asked, lifting her into his arms. 'That means I was supposed to do it all along. Can't argue with fate.'

He was pretty sure he heard Aaron say the words, "Stubborn jackass" under his breath, but he wasn't going to take the time to argue the point. It was a fairly accurate assessment.

'Do we have any more of those pills?' he asked Jennifer, who shook her head quickly.

'I mean...yes, we do,' she amended, 'But they're preventative. They don't cure.'

He swore, and Jennifer looked slightly insulted at his words. 'Well I'm _sorry_,' she said. 'But we don't have the facilities they do at HQ.'

And in that moment, David Rossi knew exactly what he had to do. Even if he didn't know why he was doing it.

*

He pulled the steel door shut, unstrapping the Time Unit, and adjusting it to fit around both of their wrists.

He didn't even know her name.

Technically speaking, by doing this, he was working so far outside the rulebook they probably should have decommissioned him retroactively. It was supposed to be an observation mission, and he'd intervened pretty heavily. Not to mention the fact that he was stretching the limits of the time machine by having it transport two people back to HQ. He wasn't even sure if it was possible.

He figured he was about to find out.

The ride was a little rougher than usual. He kept a tight hold on the woman in his arms, hoping like hell that this trip through time wasn't making her worse off. He knew he'd probably have to spend the next few days sleeping this one off. If he still even had a job.

They jerked to a stop, and he threw his hand out, pressing the button by the door. It swung open almost immediately.

'Dave, what happened? Your readings are all-' Spencer stopped talking the moment he saw that there were two people in the room, instead of just one. 'Dave...' he said quietly. 'Dave, what did you do?'

'Get her to infirmary,' Dave spat, adjusting the Time Unit so it was just on his wrist. 'There's something I need to do.'

The moment Spencer had pulled the woman free, he shut the door again, adjusting the date and time on the wrist unit. He knew this was going to work, because he'd already done it.

He slammed the green button once more, and was greeted with a, 'There are no scheduled arrivals, what are you doing here?'

It was Aaron – five years younger, but still the same Gatekeeper he had met not two hours ago. Dave didn't have time for formalities. He pulled the note from his pocket, and handed it to the Gatekeeper. 'Next time you see me, give me this. No questions. Just give it to me.' He pulled the door shut on himself, and returned to HQ.

He was unconscious by the time they opened the door.

*

Spencer greeted him when he woke, and he was very grateful that it wasn't Strauss, on one of the other superior Agents, that would have fired him sooner than asking him if he was okay.

Derek was sitting on the other side of the belt, no longer wearing a kilt. Instead, the Agent was wearing a pair of jeans, and a dark t-shirt, reading the latest issue of _Chrono Monthly_.

'I don't think he actually understands it,' Spencer whispered. 'He's just doing it to pick up chicks.'

'And boy does it work,' said Derek, shutting the magazine and tossing it onto the nightstand. 'Much more effective than kidnapping them from the timestream, at any rate.'

'She was going to die,' argued Dave. A sudden, horrific thought hit him. 'She did survive, didn't she?'

Spencer nods. 'They did manage to reverse the infection. But, she can never go back to her own time. She's listed as a casualty of the terrorist attack that you were sent there to...observe.'

'Without a body?'

'Body incinerated,' Spencer shrugged. 'Death report signed off on by an "Aaron Hotchner." He's one of the Gatekeepers, right?'

'Right,' said Dave. He looked to his left, and for the first time, noticed that she was lying in the bed next to him. She looked pale, even against the white sheets. He realized that he still didn't know her name.

'Who is she?' he asked, brain fighting against the exhaustion that was still prevalent.

'Special Agent Emily Prentiss,' Spencer revealed. 'Federal Bureau of Investigation. Graduated _cum laude_ from Yale...' He continued speaking, but once again, Dave found himself zoning out.

'Emily...' he whispered, before losing himself to unconsciousness once more.


End file.
